An image capturing apparatus includes an image sensor provided in the neighborhood of an image plane of a photographing optical system for forming the image of a subject; pupil dividing member for forming images of a pair of light beams that have passed through different pupil regions of the photographing optical system; focus detection sensors arranged two-dimensionally for photoelectrically converting images of the pupil dividing member; and a correlation calculation unit which, in order to obtain one focus measurement value from one pair of two-dimensional images generated by the focus detection sensors and extending in the pupil dividing direction of the pupil dividing member and in a direction perpendicular to the pupil dividing direction, calculates the correlation between the pair of two-dimensional images while shifting the pair of two-dimensional images in the pupil dividing direction.